linux-kernel - RE: [PATCH v6 1/5] iommu: Return -EMEDIUMTYPE for incompatible domain and device/group

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Date:   Thu, 8 Sep 2022 09:54:18 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Jason Gunthorpe <jgg@...dia.com>,
        Robin Murphy <robin.murphy@....com>,
        Joerg Roedel <joro@...tes.org>
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Subject: RE: [PATCH v6 1/5] iommu: Return -EMEDIUMTYPE for incompatible domain
 and device/group

> From: Tian, Kevin
> Sent: Thursday, September 8, 2022 5:31 PM
> > This mixture of error codes is the basic reason why a new code was
> > used, because none of the existing codes are used with any
> > consistency.
> 
> btw I saw the policy for -EBUSY is also not consistent in this series.
> 
> while it's correct to change -EBUSY to -EMEDIUMTYPE for omap, assuming
> that retrying another fresh domain for the said device should work:
> 
> 	if (omap_domain->dev) {
> -		dev_err(dev, "iommu domain is already attached\n");
> -		ret = -EBUSY;
> +		ret = -EMEDIUMTYPE;
>  		goto out;
>  	}
> 
> the change in tegra-gart doesn't sound correct:
> 
> 	if (gart->active_domain && gart->active_domain != domain) {
> -		ret = -EBUSY;
> +		ret = -EMEDIUMTYPE;
> 
> one device cannot be attached to two domains. This fact doesn't change
> no matter how many domains are tried. In concept this check is
> redundant and should have been done by iommu core, but obviously we
> didn't pay attention to what -EBUSY actually represents in this path.
> 

oops. Above is actually a right retry condition. gart is iommu instead of
device. So in concept retrying gart->active_domain for the device could
work.

So please ignore this comment.